Solvents, i.e., liquid water and/or organic such as a hydrocarbon or halogenated hydrocarbon, e.g., gasoline, turpentine, chloroform, perchloroethylene, etc., can readily damage electronic devices such as laptop computers, cell phones and personal digital assistants. Accordingly, a need exists for a label or other device to indicate whether or not an electronic device has been subjected to contact with a solvent, at least sufficient solvent to void a product warranty. This need is filled to some extent by various commercially available, single-purpose labels with a format as described in FIG. 1.
As shown in FIG. 1, solvent (here water) indicating label 10 comprises four layers. First or top layer 11 is typically a water-impervious clear plastic film, e.g., a clear polyester film, overlying water-absorbent paper layer 12. Underlying layer 12 is a layer of water-soluble ink (or dye) 13 which itself overlays a pressure sensitive adhesive layer 14. The water-soluble ink is not visible through the paper until wetted.
Water enters the structure from an edge surface of the label, not a face surface or in other words, the structure is an edge ingress label. If an edge surface of the label comes in contact with liquid water, then water will wick along the paper layer dissolving the water-soluble ink beneath the paper layer. The paper layer will absorb the solubilized ink, and the ink will become visible to an observer. The clear plastic film protects the label and keeps dissolved ink from seeping to the surface of the label and contaminating the electronic device and/or marking the user's person or clothing. If, of course, an organic solvent-soluble ink replaces the water-soluble ink, then this label will detect and report contact of the label with the organic solvent, not water.
While these single-purpose labels perform as designed, a strong interest in the electronic device industry exists for a label that can perform more. For example, an unscrupulous person could remove an activated water-indicating label from a device that has been in contact with liquid water, and replace it with an unactivated water-indicating label. One label that had both water- and tamper-indicating features could report such activity. The use of separate labels for each function would not report such activity and in any event, surface space on many electronic devices is limited thus making a dual or multi-purpose label more desirable than two or more separate labels.
One approach to a dual purpose label is to attach a small solvent-indicating label to a larger tamper-indicating label, but this approach has several drawbacks. First, the solvent-indicating label takes space on an already small label, and that space could be better used for printed information, e.g., a bar code. Second, a roll of labels with non-uniform thickness is difficult to roll uniformly. Third, the thicker portion of the label creates difficulties if print is imparted to the label using thermal transfer printing. Fourth, such a label with another label creates a very thick profile and interferes with efficient packing of a battery and other components into a thin electronic device.
Better solutions and improved formats are desired for an effective label that possesses both tamper- and solvent-indicating features.